Biochar with inherited negative surface charges derived from Enteromorpha prolifera as a promising cathode material for capacitive deionization technology

The conversion of biowaste into valuable carbon-based materials is beneficial for developing a sustainable energy economy. In this study, activated carbons (ACs) are successfully synthesized via one-step carbonization using Enteromorpha prolifera (EP) as the precursor, which is a kind of ocean biowaste causing green tides. Owing to EP's ordered anatomic texture and naturally embedded alkalis, the produced EP-derived ACs (EPACs) exhibit hierarchical porous structure without any support from active agents. Plentiful heteroatoms are also formed on surface of EPACs, endowing the carbon with good hydrophilicity and unique electronegativity. Consequently, the salt adsorption capacity and the charge efficiency of the capacitive deionization (CDI) system are improved by 12.1 % and 11.95 % respectively by replacing the commercial-AC cathode with the EPAC-800 cathode (pyrolyzed at 800 °C). The potential distribution test and the modified Donnan model simulation suggest that the hierarchical pore volume of EPAC-800 offers great desalination capacity, while its surface electronegativity optimizes the potential distribution of the two electrodes. The new knowledge gained from this work will hopefully not only establish a scalable method to utilize the EP waste, but also guide the design and manufacture of high-performance electrodes for CDI technology.